APPLICANT'S DESCRIPTION: This proposal will test the utility of a stress- inducible cellular promoter to drive expression of therapeutic genes to induce regression and immune rejection of solid tumors. The approach is based on the observation that stress proteins, known as glucose regulated proteins (GRP), are overexpressed in solid tumors, protecting stressed cells from apoptosis. The ability of the grp78 promoter is utilized to drive expression of therapeutic genes in tumors, starved for glucose and oxygen, to facilitate tumor regression. The HSV thymidine kinase gene (HSVtk) under control of the grp78 promoter is induced in stressed cells, making cells exquisitely sensitive to the action of ganciclovir (GCV). We had established that tumors transduced with a retroviral vector containing the HSVtk gene driven by the grp78 promoter regress in mice treated with GCV. Further, we have shown that immune memory is induced against the regressing tumor. These observations raise the question as to the usefulness of stress inducible promoters as a tool for gene therapy of solid tumors. The goal of this proposal is to test the affectivity of this strategy in in vivo tumor models in mice. We have shown that tumors transduced with a therapeutic gene construct regress in animals treated with GCV but the question needs to be answered whether tumors, not transduced with the therapeutic gene may regress concomitantly. Regression of non-transduced tumors requires a specific recognition event of either the adaptive cell mediated immune system or by the natural immune system. Experiments are proposed in immunocompetent animals or animals depleted of specific immune effectors. The vector, currently used to transduce tumor cells is a first generation design which has shown promising effects in vivo. We will test this promoter construct for its efficiency in various tumor models and propose to introduce modifications to this design to make it more efficient for induction of tumor regression. The modifications will include elimination of the remaining basal control elements in the grp78 promoter, used in the current construct to achieve more stringent gene expression and inclusion of therapeutic genes. Modifications to be incorporated into these constructs will include CD8O, a ligand that stimulates sensitization of T cells and GM-CSF a cytokine which stimulates antigen presenting cells with the overall goal in mind to induce a response to weak tumor specific epitopes.